1. Field of the Invention
This invention relates to a moving table assembly disposed between a table supported by a base for movement in one direction and a nut threadably engaged with a feed screw supported by the base with the axis thereof parallel to the direction of movement of the table so that there is obtained accurate displacement of the table corresponding to the rotative displacement of the feed screw.
2. Description of the Prior Art
The conventional positioning table assembly generally used is of a construction in which a nut is secured to a table guided and supported by guide means provided on a base and movable in one direction and a feed screw is threadably engaged with the nut so that there is obtained a displacement of the table corresponding to the rotative displacement of the feed screw.
Such a positioning moving table assembly has an advantage that its mechanism is simple, whereas some eccentricity resulting from an error of finishing is present in the feed screw or the bearing portion for rotatably supporting the feed screw and therefore, when the feed screw is rotated, the nut is displaced in the axial direction of the feed screw and in addition, is slightly deviated in a direction perpendicular to the axis of the feed screw. In a positioning table requiring precision, a ball screw is generally used as the feed screw and balls interposed between the feed screw and the nut are pre-pressed or pre-loaded to eliminate any back-lash of the feed screw and the nut and therefore, if there is a deviation of the nut as described above, such deviation of the nut is transmitted to the table, and with the rotation of the feed screw, a force in a compression or pull direction acts on the guide means supporting the table and thus, the sliding resistance of the sliding portion of the guide means fluctuates so that accurate sliding movement of the table cannot be effected.